In a digitally controlled inkjet printing system, a receiver media (also referred to as a print medium) is conveyed past a series of components. The receiver media can be a cut sheet of receiver media or a continuous web of receiver media. A web or cut sheet transport system physically moves the receiver media through the printing system. As the receiver media moves through the printing system, liquid (e.g., ink) is applied to the receiver media by one or more printheads through a process commonly referred to as jetting of the liquid. The jetting of liquid onto the receiver media introduces significant moisture content to the receiver media, particularly when the system is used to print multiple colors on a receiver media. Due to the added moisture content, an absorbent receiver media expands and contracts in a non-isotropic manner, often with significant hysteresis. The continual change of dimensional characteristics of the receiver media can adversely affect image quality. Although drying is used to remove moisture from the receiver media, drying can also cause changes in the dimensional characteristics of the receiver media that can also adversely affect image quality.
FIG. 1 illustrates a type of distortion of a receiver media 3 that can occur during an inkjet printing process. As the receiver media 3 absorbs the water-based inks applied to it, the receiver media 3 tends to expand. The receiver media 3 is advanced through the system in an in-track direction 4. The perpendicular direction, within the plane of the un-deformed receiver media, is commonly referred to as the cross-track direction 7. Typically, as the receiver media 3 expands in the cross-track direction 7, contact between the receiver media 3 and contact surface 8 of rollers 2 (or other web guiding components) in the inkjet printing system can produce sufficient friction such that the receiver media 3 is not free to slide in the cross-track direction 7. This can result in localized buckling of the receiver media 3 away from the rollers 2 to create lengthwise flutes 5, also called ripples or wrinkles, in the receiver media 3. Wrinkling of the receiver media 3 during the printing process can lead to permanent creases in the receiver media 3 which adversely affects image quality.
U.S. Pat. No. 3,405,855 to Daly et al., entitled “Paper guide and drive roll assemblies,” discloses a web guiding apparatus having peripheral venting grooves to vent air carried by the underside of the traveling web.
U.S. Pat. No. 4,322,026 to Young, Jr., entitled “Method and apparatus for controlling a moving web,” discloses a method for smoothing and guiding a web in which the web is moved in an upward direction past pressurized fluid discharge manifolds on either side of the web. The manifolds direct continuous streams of pressurized fluid, such as air, outwardly toward the side edges of the web to smooth wrinkles in the web. Additional manifolds are used to intermittently direct streams of fluid to laterally move and guide the web.
U.S. Pat. No. 4,542,842 to Reba, entitled “Pneumatic conveying method for flexible webs,” discloses a method for conveying a web using inner and outer pairs of side jet nozzles employing the Coanda effect to propel the web while preventing undue distortion.
U.S. Pat. No. 5,979,731 to Long et al., entitled “Method and apparatus for preventing creases in thin webs,” discloses an apparatus for removing longitudinal wrinkles from a thin moving web of media. The media is wrapped around a perforated cylindrical air bar disposed in proximity to a contact roller.
U.S. Pat. No. 6,427,941 to Hikita, entitled “Web transporting method and apparatus,” discloses a web transporting apparatus that transports a web by floating the web on air jetted from holes formed in a roller while the edges of the web are supported by edge rollers.
There remains a need for a means to prevent the formation of receiver media wrinkles as a receiver media contacts web-guiding structures in a digital printing system.